What are Web APIs?

An API stands for Application Programming Interface. A Web API is implemented by a web application server through which it makes it services available to client applications.

Think of an API as a menu in a restaurant, and the web server is the kitchen.

The menu (API) tells you exactly what you can order (the available resources/data) and how to order it (the specific URLs and HTTP methods).
You (e.g., your JavaScript application) are the customer placing the order.
The kitchen (Web Server) processes your request and sends back a response (your food/data).

A Web API (or Web Service API) is simply an API that is accessible over the HTTP protocol, the same protocol used for viewing websites. It allows different software applications to communicate with each other over the internet.

Here is a quick intro into APIs, check out the video below (3:56 min):

https://www.youtube.com/watch?v=bxuYDT-BWaI

Public vs Private APIs

There are 2 different types of APIs: public and private APIs.

An API is public when software companies publish parts of their software to be freely used by developers from the outside world. If you were to integrate the Facebook API as a login system in your application, you would be using their API as a public API.

Conversely, there are also private APIs: software companies that grant access to parts of their backend applications to internal developers only, in order to develop new services to be used either internally or for the outside world.

In reality, there are way more private than public APIs. This is because it's usually in the company's best interest to keep their code base hidden from the public eye: it would be like giving your secret recipe away for free.

Keep this in mind: in the real world programming is only a means to serving a business end. In this course you're learning how to program, to make nice-looking, well-functioning applications. However, this is always done within a business context. This is to say: does this software lead to making more money/gaining more popularity/or the achievement of any other business goal?

Important API Concepts

The Core Purpose: Communication

The primary goal of a Web API is to allow a client (like your JavaScript application) to access data or trigger actions on a remote server.

Example: A weather app (client) calls the OpenWeatherMap API (server) to get the forecast data for a city. The server handles the complex data collection and sends back a clean, structured result.

Standardized Exchange: Request and Response

Web API communication is always a two-part standardized cycle:

Step	Component	Description
1. The Request	Client sends data to Server	Your application constructs a request, which contains:

A URL (the address of the resource).
An HTTP Method (the action to perform: GET, POST, etc.).
Headers (metadata like authorization and content type).
An optional Body (for POST/PUT data). | | 2. The Response | Server sends data back to Client | The server processes the request and sends back a response, which contains:
A Status Code (e.g., 200 OK, 404 Not Found).
Headers (metadata about the response).
A Body (the requested data, usually in JSON format). |

The Standard Data Format: JSON

Nowadays, the vast majority of modern Web APIs use JSON (JavaScript Object Notation) as the format for exchanging data in the request and response bodies. (Before JSON took over, another format called XML was commonly used on the web.)

JSON is a human-readable, lightweight format that is native to JavaScript, making it the perfect choice for API development and consumption using tools like fetch.

Example of a JSON Response Body:

{
  "user_id": 101,
  "first_name": "Alex",
  "is_active": true,
  "orders": [
    { "id": 5001, "item": "Widget" },
    { "id": 5002, "item": "Gadget" }
  ]
}

REST (Representational State Transfer)

When you hear the term web API, it is almost always referring to a RESTful API.

REST is an architectural style (a set of design principles) for building Web APIs.
A RESTful API uses standard HTTP methods (GET, POST, PUT, DELETE) and structured URLs to manage resources.
The key principle: The API treats data as resources that can be identified by a URI (URL) and acted upon using the standard HTTP methods.

Specific URLs at which an API responds to HTTP requests are called endpoints. The table below gives an example of the endpoints of a RESTful API.

Action	HTTP Method	Endpoint	Parameter (id)
Get a list of books	GET	/books
Get a single book	GET	/books/{id}	42
Create a new book	POST	/books
Update book 42	PUT or PATCH	/books/{id}	42
Delete book 42	DELETE	/books/{id}	42

https://www.youtube.com/watch?v=-mN3VyJuCjM

https://www.youtube.com/watch?v=tkfVQK6UxDI

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Week 9 - Networking and APIs